Radio receiving circuit



H. H PARKER RADIO RECEIVING CIRCUIT April 28, 1936.

Filed May 29, 1926 muwmoi Patented Apr. 28, 1936 UNITED STATES PATENTOFFICE RADIO RECEIVING, CIRCUIT Application May 29, 1926, Serial No.112,516

4Claims. (Cl. 179-171) My invention relates to radio receiving circuits,the object of this invention being to provide means whereby the relayaction of electron tubes, connected in cascade, is repeated andamplified more perfectly as to wave form by their associated amplifyingdevices than by other methods usually employed.

It is well known that iron core transformers introduce considerabledistortion into otherwise satisfactory radio reception and whenresistance coupling, or other forms of direct or conductive inter-tubecoupling, is used to gain better quality of reception it is necessary toseparate the steady potential applied to the plate of one tube from thegrid of the following tube in order that the grid can be maintained byother means at the proper biasing voltage, so that the tube will operateon the linear portion of its characteristic curve and the output moreperfectly reflect the wave-form of the input.

This is usually accomplished by inserting a stopping condenser in thegrid lead and connecting the grid, by means of a high resistance usuallyknown as, a leak, to the filament. This may be connected to the filamenteither directly or through a battery, or other means, and is for thepurpose of maintaining the desired stabilizing voltage.

Now when this is done undesirable losses and. other disturbing factorsare introduced.

As an example, one of the faults in the above described combination of astopping condenser and grid leak in the input circuit of an amplifyingtube is that the stopping condenser is a r reactance against the signalwhich is a loss.

Also the value of this reactance is variable being dependent upon thefrequency of the currents passed and therefore passes a current ofhigher frequency with less reactance than a current of lower periodwhich promotes distortion of the signal. Again when a grid resistance isin shunt with the input circuit it consumes energy from the signalcurrents and it is also probable that at times the negative chargeaccumulating on the grid is dissipated too fast or too slow, dependingupon various factors, and because .of this would throw the repeatingaction of the tube'from the linear portion of its characteristic curveto a point where the tube itself would create distortion of the signal.

In order, therefore, to avoid the above mentioned faults in a radioreceiver and further to amplifyreceived signals with greater freedomfrom distortion, I have developed a system of amplification-applicableto audio frequency, radio frequency or radio beat frequency, all ofwhich may be used separately or in combination and also in combinationwith detector tubes and associated apparatus.

The attached drawing and detailed description of this method of radioreception are intended to clearly illustrate the operation andfundamentals involved, and other elements which might be desirable touse in this circuit but not essential to clearly show the scope of theinvention are not shown.

Referring to the drawing:

Fig. 1 is a diagrammatic view of a receiving system embodying myinvention.

Fig. 2 is a diagrammatic view of a modified form of receiving system butstill embodying my invention.

Fig. 3 is a still further modification of the receiving system. 1

In most cases of radio receiving systems a certain condition exists,namely, that when the inter-tube coupling device between any twosuccessive tubes in a radio receiver is direct, or conductive, and is soconnected as to offer little or no resistance to continuous currentbetween the plate of one tube and the grid of the following tube, thesteady voltage normally applied to the plate of one tube would also beimpressed upon the grid of the following tube, thereby rendering saidtube inoperative.

In order to use a coupling device of the particular type to bedescribed, with little or no continuous current resistance between theplate of one tube and the grid of the following tube, and to have the A.C. component of the plate. current impressed in as direct a manner aspossible on the grid of the following tube, the potential differencebetween the filaments of two successive tubes is at a fixed value andthe required relative voltages of the output circuit of the first tubeand the input circuit of the following tube are simultaneously obtainedby the common return of this inter-tube coupling being connected to thecorrect relative location on the source of supply (on the resistancebetween the two filaments as disclosed on the drawing).

Referring to Fig. 1, there is shown a typical receiving system in whichis provided electron tubes l, 2, 3, 4 and 5, and each tube is providedwith the usual filament, grid and plate electrodes. In tube l thefilament is designated by the numeral 6, the grid by the numeral 1 andthe plate by the numeral 8. In tube 2 the filament is designated by thenumeral IS, the grid by the numeral l0 and the plate by the numeral ll.

The usual aerial 2| with the primary induction coil 22 is grounded at23, which is the usual construction employed in radio receiving setsusing the outside aerial. While the drawing has disclosed the principleof employing the usual antennae, it is to be understood that theinvention will function as successfully wherein a loop is employed orwhere the induction coil 24 is used as a loop. A second induction coil24 associated with the primary induction coil 22 is connected into thegrid circuit of the first tube. The usual variable capacity condenser 25is introduced across the ends of the induction coil 24 for the purposeof tuning.

The filaments of the respective tubes, and referring particularly to thefilament 6, the description of which will apply to the respectivefilaments of the other tubes, is connected directly to a secondary coil26 of a transformer which has a primary 3| connected directly to thesource of supply. Similar secondaries 21, 28, 29 and 30 supply thefilaments of the respective tubes with the proper voltage tosufiiciently heat them Each filament is provided with a resistance 32across the terminals thereof, and is further provided with a central tapwhich is attached to the resistance element I2 at a point 33 thereon. Asimilar result may be obtained by tapping off from the electrical centerof the secondary windings 26, 21, 28, 29 and 30. The secondary windingsare insulated from one another as shown in Fig. 1, and are capable of adifference of potential (D. C.) being maintained between them. Theprimary winding of the transformer is shown as being a continuouswinding but this is not necessary and may be composed of separateprimaries similar to the secondaries already described.

As a means for supplying the required plate or D. C. volt-age to therespective tubes preferably rectified and filtered A. C. current issupplied to each end of a resistance element I2 or to a number of unitsconnected in series. This resistance element I2 is in communication withthe plate of each electron tube, the particular function of which willbe hereinafter explained.

As has been heretofore pointed out it has been practically impossible toconnect the plate of one tube directly with the grid of a successivetube without the introduction of proper condensers and grid leaks intothe circuit between the electrodes of successive tubes. Naturally, ifthe plate of one tube was connected directly to the grid of a successivetube and the plate potential supplied to that connection, the voltagewould be impressed not only on the plate of the first tube but also onthe grid of the following tube. This would paralyze the action of thefollowing tube so that it would fail to operate. By the introduction ofthese particular condensers and resistances a loss of amplification iscreated as well as non-uniformity of amplification due to the variableaction of these elements and thereby hinders perfect amplification.

It is my intention, as disclosed in the drawing, to connect the plate ofone tube with the grid of the following tube and to eliminate thecondensers and resistances ordinarily employed as heretofore explained.By employing a common return comprising an inductance coil I6 having oneend connected into the circuit between the plate and the grid ofsuccessive tubes I and 2, and the opposite end connected to the resistorI2 at the correct location thereon the proper plate voltage is obtained.The positioning of this end of the inductance coil I6 upon theresistance element I2 simultaneously controls the proper voltagesupplied to the grid circuit of the second tube.

The difference of potential between the plate 8 and the filament 6, D.C. component or steady value, is determined by the drop in voltage onresistor I2 between the points 33 and 36 minus the drop through theinductance coil 26 and part of the balancing resistance 32. The steadyvalue and superimposed A. C. value of voltage on the grid I0 istherefore the same as that of the plate 8 and would normally paralyzethe action of tube 2 and in order that the steady voltage rela tionsbetween the input elements of tube 2 be such as will bring this tubeinto essential operating condition, the voltage of the center of thefilament I9 is raised in a positive direction in relation to thefilament 6, by an amount approximately equal to the algebraic sum of thedifference of potential between the plate 8 and the filament 6 and thevoltage difference desired between grid Iii and filament I 9. This iscontrolled by the location of the tap 35 on the resistance element I2with respect to the location of the tap 3-3 on the resistance elementI2. By this arrangement therefore the voltage existing between points 33and 35, neglecting minor considerations, is also the sum or differenceof the voltages between the filament 6 and the plate 8 of the tube 1 Iand the filament 9 and the grid II] of the tube 2 depending upon whethera positive, negative or zero grid is wanted. Therefore the plate andgrid voltage is fixed simultaneously by the location of the commonreturn tap 36 on the resistance element l2 and this location may be oneither side of the tap 35 or it may be connected to it.

The operation and voltage adjustments as affecting the output and inputcircuits of the tubes I and 2, above mentioned, is essentially the samefor the other tubes as shown and the electrical constant and type ofinter-tube coupling employed will determine whether the tubes functionas detector, radio frequency amplifier, audio frequency amplifier orradio amplifier of a beat frequency.

It should be noted that the location of the tap 3'! on the resistanceelement I2 is shown on the far side of the filament of the tube 3. thepurpose of supplying a positive grid potential which is desirous inoperating the detector tube as this tube operates primarily as arectifier.

In Fig. 2 a similar arrangement is shown in which the principle is notaltered and the operation is essentially the same and differs from Fig.1 by the simultaneous use of resistor 40 as current supply and voltagedistributing unit to a multitube radio amplifier and multi-tube audioamplifier making the resistance element 40 common to both. Thisparticular construction effects economy of power as it means the D. C.voltage across the resistance element 40 is less than if this were notdone.

When this form of resistance is used energy is transferred from theoutput of the first amplifying group to the input of the next byinductive or capacitive means, or in any manner, which preserves thevoltage relations in the output circuit of the tube in the most positiveposition on resistance element 40 and the input voltage relations ininput circuit of the tube to which energy is transferred in the mostnegative position on resistance element 40.

In Fig. 2 tube 4| is considered as the detector This is for i tube andtap 42 is so located on the resistance element 40 to give the correctgrid bias to the grid 43, and tap 44 is so located on the resistanceelement 40 to furnish plate 45 with the correct voltage for detection.46, 41 and 48 represent respectively the primary windings, the ironcore, and the secondary windings of the ordinary audio transformer and49 and 50 represent the output terminals from the first group of tubesand 49' and 50' represent the input terminals to the second group. It isto be understood, however, that these two groups should be connectedtogether through the means of the terminals just described.

In Fig. 3 the principle of operation remains the same and when a D. C.current in excess of that required to sufiiciently heat the filamentsand of sufficiently high steady potential is applied to the terminals ofthe resistance element 50, this arrangement functions practically thesame as the.

system described in Fig. 1.

With the arrangement disclosed in Fig. 3, the filaments of therespective tubes might be considered as being connected in series or amodification of a series system, but I do not claim this arrangement asa part of my invention. In connection with this series arrangement I doclaim, however, as being new and novel and. vital to this invention, themeans of separating and maintaining the various filaments at therequired steady difference of potential between the filaments ofsuccessive tubes, as for example, between the terminals 5| and 52 inFig. 3 or as between the terminals 33 and 35 in Fig. 1.

In Fig. 3 the filament supply is taken from the resistance element 50 byvirtue of the fact that the current shunted around the filaments isinversely proportional to the respective resistances of the variousfilaments and the parts of the resistance element 50 included betweentheir terminals, such as shown by filament 55, and resistance includedbetween points 52 and 54, in which case the total resistance across theresistance element 50 is less with all filaments connected than withthem not connected, which change in resistance is immaterial as long asthe required relations exist with the filament terminals fixed.

Having thus described my invention, what I claim is:

1. In a tuned radio frequency circuit, a pair of electron tubes havingcathode, grid and plate electrodes, means for directly connecting theplate of one tube with the grid of the succeeding tube, separatealternating current circuit means for heating said cathodes, a source ofdirect current for supplying the grid and plate potentials, cathodeleads associated with said source of direct current, a coupling deviceconnected to said plate and grid connecting means and associated withsaid source of direct current, and a variable tuning element in shuntwith said coupling device.

2. An amplifying device comprising the combination of first and secondamplifying tubes, each tube having cathode, anode and controlelectrodes, means for directly connecting the anode of said first tubewith the control electrode of said second tube, a source of directcurrent, a potentiometer connected thereto for supplying operating andbiasing potentials for said tubes, means including a coupling elementconnected between said first means and said potentiometer to supply thedesired output and input biasing potentials, leads to the remainingelectrodes of said tubes from points of said potentiometer positionedrelative to each other and to said potential supply means to furnish thedesired operating and biasing potentials between the cathode and anodeof said first tube and the cathode and control electrode of said secondtube, respectively; a power transformer having a single primary windingand a plurality of independent, insulated secondary windings, and leadsconnecting said secondary windings to the respective cathode terminals.

3. An amplifying device comprising a potentiometer having its terminalsconnected to the opposite leads of a direct current supply source,

a plurality of vacuum tubes each having an anode, a grid and a cathode,a direct current connection between the anode of one tube and the gridof the succeeding tube, connections between the tubes and thepotentiometer at such points that the voltage on said last named grid,due to anode current, is compensated; other vacuum tubes each having ananode, cathode and grid, a direct current connection between the anodeof one tube and the grid of the succeeding tube and connections betweenthe tubes and the potentiometer at such points that the voltage on saidlast named grid due to anode current is compensated, said last namedpotentiometer connections being made to points on said potentiometerhaving substantially the same voltages as those to which said firstmentioned potentiometer connections are made.

4. The combination defined in the preceding claim in which the firstnamed plurality of tubes serves to amplify modulated radio frequencycurrents and in which detecting means is interposed between this groupand said second group whereby the tubes of the second group serve toamplify currents of the modulation frequency.

HOWARD H. PARKER.

